Russian Journal of Physical Chemistry A最新文献

The Fe/MgAl₂O₄ catalysts modified with In were prepared by joint impregnation of aluminum–magnesium spinel with solutions of metal nitrate salts. Data on the adsorptive and reductive properties of the catalysts obtained by the in situ magnetic method, XPS, thermolysis, and IR spectroscopy of adsorbed CO are compared. It was established that the presence of indium in the catalyst inhibits the reduction of iron oxides to magnetite, as well as the stage of water removal from the catalysts and the decomposition of metal nitrates. It was shown by IR spectroscopy that the main adsorption sites are the structures that include Fe²⁺ cations.

The confinement effect of carbon nanotubes plays a significant role in the field of catalysis. A bamboo-structured N-doped carbon nanotubes (NCNT) encapsulated PdCo nanoparticles (PdCo@NCNT) was prepared by pyrolysis method with melamine as carbon and nitrogen source. The preparation conditions of PdCo@NCNT and the growth mechanism of NCNT were studied. TEM test showed that the PdCo nanoparticles are fully encapsulated by the graphitic shell on the top of carbon nanotubes. There exists electron transfer between Pd and Co, and a bimetallic PdCo active center with electron-rich Pd and electron-deficient Co formed. PdCo@NCNT exhibited higher catalytic activity for furfural hydrogenation than Co@NCNT. PdCo@NCNT with PdCo encapsulated within NCNT showed better furfural hydrogenation activity and reusability property compared with PdCo/NCNT with NCNT external loading method.

The adsorption, electronic, and thermodynamic properties of the 2 × 2 × 1 and 3 × 3 × 1 supercells of the binary compounds (({{{text{A}}}_{n}}{{{text{B}}}_{m}} = 4{text{H}}- {text{SiC}},) ({{alpha }}{kern 1pt} {text{ - }}{kern 1pt} {text{L}}{{{text{i}}}_{2}}{{{text{C}}}_{2}},) ({text{L}}{{{text{i}}}_{n}}{text{S}}{{{text{i}}}_{m}})) of the Si–C–Li system were studied using the density functional theory (DFT). The theoretical capacity of the 4H–SiC hexagonal polytype was found to exceed that of graphite (370 mA h/g) used as an anode material for lithium-ion batteries. The crystalline compounds ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) have electronic conductivity. The DFT calculations used the exchange-correlation functional within the framework of the generalized gradient approximation (GGA PBE). The parameters of the crystal structure, the adsorption energy of the ({text{L}}{{{text{i}}}_{{{text{ads}}}}}) adatom on the 4H–SiC substrate, the electronic band structure, and the thermodynamic properties of the supercells of ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) compounds were calculated. The thermodynamically favorable position of ({text{L}}{{{text{i}}}_{{{text{ads}}}}}) and the stable configuration of the 4H–SiC〈Li_ads〉 supercells were determined. The DFT calculations of the enthalpy of formation of ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) compounds in the Si–C–Li ternary system were performed. The calculated characteristics of ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) agree with the experimental data. The equilibrium connodes in the concentration triangle of Si–C–Li were established using the standard thermodynamic potentials of ({{{text{A}}}_{n}}{{{text{B}}}_{m}}) compounds and the changes in energy in solid-phase exchange reactions between these compounds. An isothermal section of the phase diagram of Si–C–Li at 298 K was constructed.

In this work, spinel magnesium manganese oxides MgMn₂O₄ were successfully synthesized via a sol-gel method followed by calcination. In order to alleviate the particles aggregation of MgMn₂O₄, carbon spheres (CS) as the sacrificial template were introduced during the sol-gel synthesis process. The addition of CS templates at weight ratios of 5 and 20% relative to Mg²⁺ respectively yields products characterized by well-dispersed nanoparticles and hollow porous nanocages. Galvanostatic charge-discharge tests demonstrated that the MgMn₂O₄ with a 5% CS template could deliver the maximum discharge capacity of 155.5 mA h/g, while still maintaining a reversible capacity of 115 mA h/g after 100 cycles at a current density of 100 mA/g. The MgMn₂O₄ derived from a 20% CS template displays a hollow porous nanocages, with a capacity slightly lower than that of the 5% CS template. However, it exhibits excellent cycling stability, especially at a high current density of 300 mA/g, where after 250 cycles, the capacity retention rate remain as high as 93%.

In this paper, Fe₂TiAl–Fe₂Ti alloy was prepared by arc melting method, and its corrosion and tribocorrosion behaviors were investigated in detail. The results showed that Fe₂TiAl–Fe₂Ti alloy exhibited better corrosion and tribocorrosion resistance compared to 0Cr18Ni9 stainless steel in 0.5 mol/L H₂SO₄ solution due to the formation of TiO₂–Al₂O₃–Fe₂O₃ protective layer on the surface. Compared to static corrosion, the alloy exhibits a lower corrosion potential, higher corrosion current, and noticeable fluctuations in the polarization curves under sliding conditions. With the onset of sliding, the OCP value of the alloy decreases and the current density increases, with an inversely varying relationship between the friction coefficient and the OCP, indicating a significant wear-accelerated corrosion effect. At higher potentials, the wear volume of Fe₂TiAl–Fe₂Ti alloy and 0Cr18Ni9 stainless steel increases, indicating that corrosion accelerates wear.

Novel graphdiyne (GDY) materials with tunable electronic and nonlinear optical (NLO) properties are always desirable for material development. Herein, we conducted a comprehensive prediction of silagraphdiyne (SiGDY) with the adsorption of alkali metals (M) and superalkalis molecules (M₂F) onto its surface, and their geometric structures, electronic properties, charge transfer and nonlinear optical responses were systematically studied. Our calculations demonstrate that the M/M₂F molecules can be adsorbed stably on large delocalized SiGDY surfaces reflected by high binding energies. Notably, the SiGDY can accept almost an electron transferred from M/M₂F, forming strong intramolecular charge-transfer (CT) process, while the reduced vertical ionization potentials (VIP) create the necessary conditions for enhancing the NLO response. Furthermore, it is found that both the substitution of silicon atoms within GDY and the adsorption of M/M₂F onto SiGDY significantly modulate electronic properties, and narrow the HOMO–LUMO gaps of complexes. More interestingly, the adsorption of M/M₂F on SiGDY enhances remarkably the first hyperpolarizability (β_tot) of complexes, especially for M@SiGDY, of which Li@SiGDY possesses the exceptionally large β_tot value (~7.65 × 10⁵ a.u.), further explained by two-level model. The present findings show that the functionalized SiGDY materials can be considered as promising candidate of novel carbon-based NLO nanodevices for future applications.

The electrical conductivity of ionic liquids (ILs) is an important figure of merit for any electrochemical application. In this regard, we measured electrical conductivities of N,N-dimethylethanolammonium based PILs at different temperatures from T = 293.15–323.15 K, and the results are discussed in terms of the effect of temperature, hydrophobicity, and H-bonding abilities of ions on conductivity. The investigation into alterations in the electrical conductivity of ionic liquids (ILs) in both polar protic and aprotic solvents holds significant importance for advancing the industrial applications of IL solutions. To broaden the potential applications of ILs, we conducted measurements of the specific conductivity (κ) in binary mixtures involving N,N-dimethylethanolammonium carboxylates [DMEA] [Carboxylates], a protic ionic liquids (PILs), with water, ethanol, and acetonitrile at 298.15 K. The aggregation behavior of the PILs in various solvents was studied by determining the critical aggregation concentration (CAC), and standard Gibbs energy of aggregation ((Delta G_{{text{a}}}^{^circ })). The findings from studies on the electrical conductivity of mixtures involving [DMEA] [Carboxylates] with molecular solvents are analyzed with a focus on ion-solvent interactions. The discussions encompass the impact of hydrophobicity, as well as the influence of H-bonding abilities exhibited by both the ionic liquid (PIL) and the solvent on the aggregation behavior observed in the mixtures.

The isobaric heat capacity of pyrochlore gadolinium titanate Gd₂Ti₂O₇ is measured in the 2–1825 K range of temperatures. Thermodynamic functions (entropy, enthalpy change, reduced Gibbs energy) are calculated using consistent smoothed values of heat capacity. The Gibbs energy of the formation of Gd₂Ti₂O₇ from oxides in the high temperature range is estimated.

The phase formation of neodymium tungstate Nd₂WO₆ from mechanically activated oxides was studied in a wide temperature range: 25–1600°C. Conditions for the formation of various polymorphic modifications were determined: low-temperature orthorhombic β-Nd₂WO₆ and δ-Nd₂WO₆ (P2₁2₁2₁ (no. 19)); high-temperature monoclinic Nd₂WO₆ (C12/c1 (no. 15)). Optical absorption spectra were studied for polymorphic ceramics with a nominal composition of Nd₂WO₆. Differences in the spectra of δ-Nd₂WO₆ and monoclinic Nd₂WO₆ were detected. Both modifications (δ-Nd₂WO₆ and monoclinic Nd₂WO₆) showed proton conductivity with activation energies of 1.05 and 1.06 eV, respectively. For the Ca-containing solid solution with a monoclinic structure (Nd(_{{1 - x}})Ca_x)₂WO(_{{6-delta }}) (x = 0.01), whose overall conductivity increases compared to that of pure monoclinic Nd₂WO₆, hole conductivity predominates in air.

In this work, the shear viscosity (η) of the liquid alkali metals including Rb, Cs, and Na is determined based on the Stokes–Einstein’s equation by an improved mean spherical approximation theory using an effective square-well potential relation for intermolecular interaction in a wide range of densities and temperatures. In this way, the PVT data and the linear isothermal regularity equation of state are used to determine the radial distribution function at a contact point at any thermodynamic state. The results obtained showed that the calculated values for viscosity increased strongly with increasing density and increased slightly with temperature. A reasonable agreement has been found between the calculated values of η and their available experimental data. Furthermore, a correlation relation between the effective molecular diameter and the temperature was found and the order of magnitude and sign of the coefficients were determined.